1. Field of the Invention
Embodiments of the present invention are directed to power inputs and outputs used in a power system, and more particularly to a power input and a power output that may be selectively configured to accommodate changes in the power requirements of an uninterruptible power supply.
2. Discussion of Related Art
The use of an uninterruptible power supply or “UPS” to provide power to a critical load is well known in the art. The UPS is designed to protect electronic equipment from utility power blackouts, brownouts, sags and surges. The UPS may also protect electronic equipment from small utility fluctuations and large disturbances. In most configurations, the UPS provides battery backup until utility power returns to safe levels or the batteries are fully discharged. Known uninterruptible power systems include on-line UPSs and off-line UPSs. On-line UPSs provide conditioned AC power as well as backup AC power upon interruption of a primary source of AC power. Off-line UPSs typically do not provide conditioning of input AC power, but do provide backup AC power upon interruption of the primary AC power source. On-line UPSs of the type described above are available from American Power Conversion Corporation, West Kingston, R.I. under a variety of different trade names. In certain configurations, a UPS may include an input circuit breaker/filter, a rectifier, a control switch, a controller, a battery, an inverter, and a bypass switch. The UPS also may include an input for coupling to an AC power source and an output for coupling to a load.
The on-line UPS as described may be configured to operate as follows. The circuit breaker/filter receives input AC power from the AC power source through the input, filters the input AC power and provides filtered AC power to the rectifier. The rectifier rectifies the input voltage. The control switch receives the rectified power and also receives DC power from the battery. The controller determines whether the power available from the rectifier is within predetermined tolerances, and if so, controls the control switch to provide the power from the rectifier to the inverter. If the power from the rectifier is not within the predetermined tolerances, which may occur because of brownout or blackout conditions, or due to power surges, for example, then the controller controls the control switch to provide the DC power from the battery to the inverter. The inverter of the UPS receives DC power and converts the DC power to AC power and regulates the AC power to predetermined specifications. Depending on the capacity of the battery and the power requirements of the load, the UPS can provide power to the load during brief power source dropouts or for extended power outages. The bypass switch is used to provide a bypass of UPS circuitry to provide the input power directly to the output. The bypass switch may be controlled by the controller to provide bypass of the UPS circuitry upon a failure condition of the UPS.
To provide further power redundancy, it is known to use a second power source to supply power to a bypass switch of a UPS from a second source of AC power. Systems of this type are often referred to as dual main systems, which are similar to the UPS described above except that it includes a second input to couple to a second power supply. The dual main UPS may include a bypass switch that selectively couples the second input directly to the output of the UPS. In dual main systems, typically, a utility power source is coupled to the first power input of the system and a backup power source, such as a generator or utility power from a different grid, is coupled to the second power input of the system. Upon failure of the utility power source, the power system is able to continue to provide power to a load using the battery mode of operation of the UPS, while the generator is powered on and brought to full output voltage. Once the generator is on line, the power system can continue to provide output power in a bypass mode for an extended period of time from the generator.
Power inputs and outputs for such systems are usually selected based on the user requirements for the particular UPS. For example, for systems requiring single phase input and single phase output, a UPS is selected to meet this requirement. Similarly, for systems requiring either three phase input and single phase output, or any other combination of input and output phases, a UPS meeting this requirement is selected. If power requirements change, a user must acquire a different UPS to meet the new requirement.